Due to the development of communications systems, various types of wireless terminals have been introduced to consumers such as companies and individuals. Current mobile communications systems belonging to the 3GPP family, such as long-term evolution (LTE) and LTE-Advanced, are high-speed, high capacity communications systems that have grown out of voice-centric services. These systems may transmit and receive various types of data, such as video data or wireless data. Thus, it is necessary to develop technologies allowing high capacity data to be transmitted at rates similar to those of wired communications networks. As deployments such as a plurality of cells or a plurality of small cells are introduced, a technology and a method able to apply carrier aggregation (CA) in a variety of deployment scenarios are required. In the meantime, a terminal may communicate with a base station using a variety of cells. In this case, the plurality of cells configured for the terminal may be divided into a primary cell (PCell) and one or more secondary cells (SCells) depending on the functions thereof. For example, the PCell provides a security input, is not changed without a handover process, and may transmit a control channel for an uplink (UL). One or more SCells may be configured as a set of serving cells together with the PCell, depending on user equipment (UE) capability.
In a joint operation in which the duplex modes of the PCell and the SCell are different, the overall efficiency of the entire network is influenced by how to set up timing of UL hybrid automatic repeat request-acknowledgement (HARQ-ACK).